At last, the truth:
The majority of philosophers expressed the view that ethicists do not behave better than non-ethicists. Ethicists themselves were about evenly divided between saying ethicists behave better and saying they behave the same. Non-ethicists were about evenly divided between saying that ethicists behave better, the same, and worse.
More useful would be to know about the differences between Kantians, utilitarians, and virtue ethicists. Based on my utterly non-scientific, anecdotal method, my conclusion is that you're safest with utilitarians and virtue theorists, and in mortal danger around Kantians (it's that combination of dogmatic rectitude and lack of judgment, I guess--or to quote Geuss again, "The Kantian philosophy is no more than at best a half-secularized version of...a theocratic ethics with 'Reason' in the place of God" [Outside Ethics, p. 20]). I assume some Experimental Philosophers will tackle this weighty matter next.
UPDATE: Professor Schwitzgebel (UC Riverside) observes:
I have noticed that everyone I've spoken to so far who thinks there are differences in ethical character between Kantians, utilitarians, and virtue ethicists thinks the Kantians are the worst of the lot. I'd be interested to hear readers' thoughts about this.